Hi guys, I seem to finally have gotten this new bird up and running almost perfectly. She idles in drive around 600 tack doesn't jump anywhere, shifts beautifully, accelerates great, hesitation is gone, but now she back fires every once in awhile from what seems like the intake, at low rpm when accelerating, and shes cold.

After the engine reaches 220/230 temperature the backfires stop almost completely, likewise they only seem to happen in the 10-30mph range, and anything after that works beautifully.

We have new plugs/wires/cap/rotor/Engine Coolant Sensor/Air Filter/Fuel Filter/IAC and throttle body has been cleaned out, TPS is adjusted to .54 and seems to go through range fine.

The only thing I haven't checked is the timing, and I'm at a loss as to why if the timing was off, this would decrease as the engine got warm, and isn't present at higher speeds.

Would a sensor of some sort cause this, or a vacuum leak somewhere?

Thanks

 

sounds like an electrical problem or possibly a timming issue, but thats pretty warm to be running at 230. mine stays at a constant 180

 

Hmm, well it pretty much goes up to 220/230 quickly, I think it has a 180 thermostat, it only has 1 electric fan which usually kicks on pretty quickly.
Even on the highway it stays around 220, sometimes it will dip down to 180/190 but it seems rare.

 

the enigne temp i dont think has anything to do with the backfiring, but i just think thats kind of warm to run at, even though alot of these cars run very warm compared to others.

 

Yeah I really think this is a sensor problem somewhere, I just ran the car for about 80 miles, and after it warmed up(5 minutes or so) there was no backfiring/hesitation at any rpm. Everything shifted and flowed great, no pinging, acceleration was good, its just when its cold it seems.

I also agree with the heat thing, but I'm not necessarily sure of a way to bring it down easily, and then there is the issue of open/closed loop as well right?

 

So I'm wondering if this could be a weak coil, and it takes the car getting hot to cause all the fuel to combust properly. Thats probably a long shot, but it almost makes sense to me hotter engine, should mean easier time igniting fuel, which if I had a weak spark could lead to a cold engine backfiring maybe.

As to my heat issues, I think I figured that out, I'm missing the Air Dam.

 

yes the air dam makes a world of a diffrence.

but as for the back firing, i would suggest just going and tryting some new plugs/wires/coil. unless you already bought new stuff. but it really sounds like an electrical problem.

 

Cap/Rotor/Wires/Plugs have all been replaced in the last 2 days, the only thing left is really rebuilding/replacing distributer or replacing the coil/ignition module. It just seems very odd that after the engine has gotten warm the problem goes away.

 

yeah that is kind of weird, is your check engine light on when you start it?

 

Nope, no check engine light. She starts up on turn of key and runs great, just backfires occasionally when first running, after a few minutes it completely goes away.

 

Open/closed loop shouldn't cause these problems. This is only to let your o2 sensor get to temp before reading it, until then the ECM uses pre-programmed settings for fuel (rich for easy start and fast warmup). If the car is to temp and/or running for 3 min, you should be ok.

Here's the low down...
FAQ's

 

So I did a bit more trouble shooting today, and with the engine cold i was getting popping/backfire and quite the bit of gas/exhaust smell. I shut off the engine, and pulled the MAF sensor connector off. Started back up, and went through the various RPM's quick accelerations/let offs/constant and got zero popping and backfiring. I then hooked it back up, and tried again and got nothing :/ Would a flacky/loss MAF sensor or connector cause this?

I also noticed unfortunately a kinda whining/wispy sound from under the car so im thinking I have some exhaust problems or my Cat has problems i'm guessing. Would a screwed up CAT cause popping/backfire, I still in general find this strange, cause I only notice it when its cold/low speeds.

 

I had this same problem with an '87 Camaro I had. I finally tracked it down to the IAT (Intake Air Temperature) sensor - it was feeding the computer false readings causing problems with the fuel mixture until the engine warmed up, which at that point, the engine runs in closed-loop mostly, going off of the O2 sensor for mixture adjustment.

The IAT is an inexpensive part. Maybe the IAT is causing your problems as well...

 

Where is the IAT located?

 

It is located on the intake tube. I had this happen on my 89rs with the 2.8 mpfi and when i disconnected the mass air sensor it would not miss on accel when cold.

 

Hello,
You could unplug the temp sensor and see how it drives....I had the backfiring thing happening with my new setup and it turned out to be a problem with the new distributor. It's a nice billit aluminum with a module. Anyway It turned out that the reluctor was out of alignment with the magnet. The timing would be more advanced when the engine was cool...and the spark would try and jump a huge gap from the tip of the rotor to the post and most times would jump to the next cylinder. Actually by unplugging the temp sensor or the EST connector....the ignition runs off the module without ECM assistance with limited timing which in my case the backfiring would stop.
If you what more info on how to troubleshoot this specific problem ...let me know. My ride is running great now!!